The invention relates to a movable lens mounting for an electrodynamic device for recording on and/or scanning optical discs by means of a radiation spot, i.e., a focused beam of electromagnetic radiation. The device comprises a frame with supporting means for guiding the, which lens mounting comprises a first part which cooperates with said supporting means and a second part which is movable relative to the first part and which comprises a mount for a lens system for focusing the radiation beam. Connecting means movably connect the first part and the second part to each other.
The invention also relates to a method of manufacturing a movable lens mounting for an electrodynamic device as described above.
Such a lens mounting and method of manufacturing a lens mounting are disclosed in Netherlands patent application 8204981 to which U.S. Pat. No. 4,443,721 corresponds.
The known lens mounting is used in an electrodynamic device in which the lens system is translated along a radial path relative to an optically readable disc which is rotatable about an axis of rotation. The supporting means of the frame comprise two guide rods along which the lens mounting can be translated by means of sleeve bearings arranged on the first part of the lens mounting. The frame also comprises two stator magnets which extend parallel to the guide rods, two actuator coils being arranged on the first part of the lens mounting in the field of these magnets. The second part of the lens mounting carries the lens system, the optical axis of which extends transversely of the optically readable disc. The second part of the lens mounting together with the lens system mounted thereon is movable relative to the first part of the lens mounting along the optical axis. The aforesaid translation of the lens mounting relative to the disc and the movement of the second part of the lens mounting along the optical axis are necessary to enable the movements of the optical disc to be followed with a radiation beam focused into a radiation spot by the lens system.
In the known construction of a lens mounting the second part thereof is movably mounted relative to the first part by means of two pairs of blade springs which are secured to the first and second parts of the lens mounting the means of bolts. Actuator coils are arranged on opposite sides of the second part to cooperate with the stator magnets to provide electrodynamic driving of the second part of the lens mounting along the optical axis of the lens system.
During the manufacture of a lens system of the type described above it is essential that the two parts of the lens mounting are positioned accurately relative to each other in order to ensure that the optical axis of the lens system of the lens mounting, when incorporated in an electrodynamic device, is perpendicular to the recording surface of the optical disc. A misalignment may result in an oblique position of the optical axis of the lens system relative to the recording surface of the optical disc, which causes a change in the light spot which is imaged on the recording (or scanning) surface of the disc. During manufacture of the lens mounting it is therefore necessary to position the second part accurately relative to the first part, after which the two parts are secured to each other by means of bolts. Particularly if large quantities of lens mountings are to be manufactured, these positioning operations, which are labor intensive, incur increased costs of manufacture.
The invention aims at providing a lens mounting and a method of the kind described above, which do not have the noted disadvantages of the previously known constructions.